In WDM optical networks, TDM is utilized to obtain time slots by separating, by a prescribed period of time, a communication bandwidth (an amount of data that can be communicated in units of time) of optical lines and to assign the obtained time slots to demands, and thereby the demands are accommodated in the optical lines. In the explanations below, a WDM optical network is also referred to as a network. Also, a communication bandwidth is also referred to as a band. Further, an optical line is also referred to as a line. A time slot is also referred to as a slot.
WDM is an abbreviation for Wavelength Division Multiplexing. In a WDM optical network, wavelength division multiplexing is conducted so that a plurality of optical lines are included in an optical fiber. TDM is an abbreviation for Time Division Multiplexing.
Demands are requests for the use of resources in a network in which a station serving as a starting point and a station serving as an ending point and a requested band are specified by users. Optical lines are lines that are used for optical communications for which optical-line routes connecting a station serving as a starting point and a station serving as an ending point are determined. In the explanations below, optical-line routes are also referred to as routes. Also, a station serving as a starting point is also referred to as a starting station. A station serving as an ending point is also referred to as an ending station.
When a demand is to be accommodated in an optical line in a network, a network design device 1 as illustrated in for example FIG. 1 is used. Starting the operation of a network 101, the network design device 1 sets an optical-line route of optical lines that accommodate demands in such a manner that resources (node devices 111 through 117 and links 121 through 126) of the network 101 are utilized effectively. Then, the network design device 1 accommodates demands in optical lines that pass through a set optical-line route. In the explanations below, an optical-line route of optical lines that accommodate demands are also referred to as routes of demands. Accommodation of demands in optical lines in a network is also referred to as accommodation of demands in a network. Also, when the node devices 111 through 117 are not discriminated from each other, they are also referred to as node devices 110. Further, when the links 121 through 126 are not discriminated from each other, they are also referred to as links 120.
When for example a demand requesting the use of a band between stations A and E has been given, the network design device 1 sets a short route of the demand as illustrated in FIG. 2, and accommodates the demand in an optical line 201 in the set route. Thereby, the network design device 1 conducts designing that utilizes resources of the network more effectively than for example a case where the demand is accommodated in an optical line 202, which passes through an optical route longer than the optical line 201.
The network design device 1 uses for example the switching function of the node device 110 that is provided in a station, and thereby assigns slots of optical lines to a demand. Thereby, the network design device 1 can change a route of a demand by switching optical lines that accommodate the demand. When a network is based on OTN (Optical Transport Network), the switching function is implemented by for example the ODU (Optical Data Unit)-XC (Cross Connect) function.
In networks during operations, it often becomes a situation where an optical line that accommodates a demand is changed due to changes in the demand, changes in network topologies and changes in the network configuration and resources in the networks are not utilized effectively. As an example, there is a situation where a route of a demand is made longer by making a detour as illustrated in for example a network 300 illustrated in FIG. 3A.
In such a case, the network design device 1 conducts reoptimization of a route of a demand in order to utilize resources of the network effectively, and executes a process of shortening the route of the demand. As an example of this, there is a process of shortening a route of a demand by referring to information representing the starting and ending stations contained in the demand in the network 300 as illustrated in FIG. 3B. Thereby, the network design device 1 reduces the number of slots to be used from (11 spans×4) slots illustrated in FIG. 3A to (5 spans×4) slots illustrated in FIG. 3B so as to utilize the resources effectively. Also, in FIG. 3, demands D5 through D8 are demands that resulted from changing the routes of demands D1 through D4. In the explanations below, a process of changing a route of a demand for shortening the route of the demand is also referred to as a reoptimization process.
As another related technique, there is a virtual network management system that includes a parameter determination unit, a priority degree calculation unit and a virtual node determination unit, and that determines a physical node generating a virtual node in response to a generation request of a virtual network. The parameter determination unit determines a weighting coefficient for the difference between a request position of a virtual node and a physical node position at the time of the priority degree determination of the physical node. The priority degree calculation unit uses a physical node state, a physical link state, a weighting coefficient determined by the parameter determination unit, a request position of a virtual node and a physical node position so as to calculate a priority degree with respect to the physical node. The virtual node determination unit determines a physical node that generates a virtual node on the basis of the priority degree calculated by the priority degree calculation unit (For example, Japanese Laid-open Patent Publication No. 2012-199644).
The network design device of the above-described communication technique has a problem that for example increase in the number of demands for which changing of routes is considered in reoptimization of routes of demands leads to increase in loads of the calculation process in the reoptimization process.